Abstract
Spatial and electronic structure of possible isomers/conformers of three α-substituted β-ethoxyvinyl trifluoromethyl ketones with general formula F3CCO–CR=CH–OC2H5, where R = H (I), R=F (II), and R = CH3, (III), their ability to form H-bonds with two secondary amines, namely, diethyl amine (1) and bis(methoxyethyl)amine (2) have been studied. It was shown that all studied α-substituted enones are E-isomers forming predominantly three conformers, viz E-s-E-s-E-trans, E-s-Z-s-E-trans, and E-s-Z-s-E-gosh, percentage of separate conformer depending not only on environment but also on steric and/or special (repulsion) interaction between α-substituent and trifluorocarbonyl group. Hydrogen bonding ability evaluated in thermodynamic scale of hydrogen bond basicity revealed that pKHB values of each conformer strongly depends on steric and/or effective charge change on carbonyl oxygen due to influence of α-substituent. Formation of H-bonded ternary complex between enone conformer and secondary amine changes electron density distribution in conformer conjugated chain, reducing positive charge on Cβ and thus changing conformer electrophilicity. On the other hand cooperativity effect in amine dimer increases net charge on amine nitrogen thus enhancing amine nucleophilicity.
Published Version
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